Electrical "wiring" of redox enzymes, a novel basis for making biosensors, provides a powerful method of directly electrically sensing lactate. Biosensors based on the wired enzymes have advantages in accuracy, sensitivity, speed, no leachable components, low sensitivity to variation in oxygen partial pressure, insensitivity to interferants, miniaturization (high signal level and small sample size), and high stability. Lactate has been demonstrated to be the best indicator of inadequate tissue oxygenation, superior to oxygen measurement. Lactate monitoring has been demonstrated to be necessary in the prediction, diagnosis and treatment of hypoxia, sepsis, intra and postoperative surgical illnesses, organ failure, adult respiratory distress syndrome and cardiogenic shock. The specific aim of the Phase II research is to develop prototype sensors for use in critical care in vitro blood gas/electrolyte analyzers, in vivo catheters (e.g., Swan-Ganz catheters) and microdialysis systems (for biomedical research). Blood gas monitors are commonly used to measure oxygen in the pulmonary artery during and after surgery. No commercial in vivo lactate sensors exist today. Existing in vitro lactate analyzers are relatively oxygen sensitive, large, inaccurate, and/or require sample dilution.